Convection reactor



March 22, 1960 R. P. HAMMOND EI'AL 2,929,767

CONVECTION REACTOR 3 Sheets-Sheet 1 Filed June 6, 1956 mm w Md D r RMM 5 March 22, 1960 RHAMMOND ETAL 2,929,767

CONVECTION REACTOR Filed June a, 1955 3 Sheets-Sheet 2 INVENTOR. R. Phil/p Hammond L0. Percival King /6M4. fidw Cold R. P. HAMMOND ETA!- 2,929,767

Mal-ch 22, 1960 CONVECTION REACTOR 5 Sheets-Sheet 3 Filed June 6, 1956 53 8mm m W \QEQ m W/ TNESSES "ea'se in recovery of spent fuel.

} 52.959.1613 CONVECTION ma ma R. Philip Hammond and L. DJPercivalKing, Los Alamos, N. Mere, assignors to the Unite'd States of America as represented by'the United States Atomic Energy Commission p Application .lunc 6, 1956, Serial-No. 589,836

2 Claims. cram-r932) The present invention relatesto nuclear reactors and more particularly to homogeneous nuclear reactors utilizing a liquid fuel. r

The nuclear reactor'of the present invention is an im proved reactor of the homogeneous type and is described as particularly. suitable for use in the production of power Where a compact,."simple, reliable, portable reactor,

capable of safe unattended operation, is required.

Homogeneous "reactors of theflPrior art generally require extensive control and monitoring facilities, thereby necessitating the presence of an operator at alltimes. The reactor of the present invention utilizesconvection circulation and thereby eliminates complicated circulating :specification, wherein:

apparatus which-must be constantly monitored for liquid fuel-leaks'and'which requires constant mechanical surveillance. Further, the presentinvention uses an internal. heat exchanger which is not located in the critical region, 3

but which located inqthe same pressure vessel as the critical region. Thus there isno necessity for handling the hot liquid fuel outside. of the reactor pressure vessel during normal operation. The liquid fuel which is utilized in the reactor of the present invention eliminates the necessity: for extensive radiolytic ,gas recombination apparatus. It is also the advantage of this reactor that no control rods are required. The reactor of the present invention also, witlioutany movable mechanical appapressure and shuts itself down if-the pressure exceedsja predetermined safe operating value. Thesel e'numerated factors result ina reactor which is materially simplified megawatt region. Theipresent invention provides for the I removal of heat from the critical region by a convection system which moves the liquid fuel up a tube and returnsit through the surrounding annulus which contains the heat exchanging apparatus. Thefact' that the liquid-gas interface is not in the critical region means that.,disturb ances. of the liquid surface will have a reduced effect upon the power and neutron level. The reactor can be primarily controlled by its'negative. temperature coefficient of reactivity and the power level can be controlled by regulating the flowof "cooling fluidthrough theheat exchanger apparatus-j f Therefore it is anfobject of the present invention to provide a homogeneous nuclear reactor which is relatively .inexpensive to build, small Iin 'siz'e,-"compact in arrangerrient and which will reliably operate without anoperator in constantattendanc'e' i "i locations.

T Type Neutron energy" 40 ratus, automatically regulates itself to the condition'of criticalityduring moderate variations in temperatureand Heat exchanger E lux in critical region:

. Another object'of the presenti invention istoprovide a homogeneous nuclear reactor which is of such size and simplicity thatitlmay be readily; transported to remote A further object ,of the presentinvention is. to provide such a homogeneous nuclearireactoriwhich does not require the use of controljrods or extensive recombination apparatus either exterior to or within the reactorvessl.

'A still further object of the present invention is to provide ahomogeneous nuclear reactor Wherein'no mechanical fuel circulating apparatus is utilized and in which the liquid fuel is asolution of uraniuniiphosphate and f phosphoric acid in water. V v A stillfurther object of the present:invention Is to provide a method without movablemechanicalapparatus for removing theliquid fuel automatically from thereactor vessel when safe internal pressures are exceeded.

Qtherobjects and advantages of the present invention will become more apparent from the following description including thedrawings, hereby made a part :ofthis 1: .Figure l is asectional view ofjithepreferred' embodi.

'ment of the present invention ponents thereon; v i I p Figure 2 is' alschematic'view of thepreferred embodishowing the internal com- "ment of the presentinvention showing the. circulation of the liquid fuelland the reflector arrangement; 7

Figur'el3 is a schematic diagram of the liquid fuel "iandling system. 7 30' SUMMARY :OF :REACTORI SPECIFICATIONS OF PREFERRED. EMBODIMENT Homogeneous. 7 Thermal.

Power 1 megawatt. Fuel U0 (enriched U dissolved in HsPOn operated with 200 psi. hydrogen overpressure.

Moderator Water. HsPOa- Refiecton Grapl1ite 7 Solution: i

Composition: a 0,3 M UO in'I7,5 My (95%) HaPO4. Operating vo1ume 97.4 lite-rs. Cold yolu1ne 82.5 liters;

Power densityn 16 law/liter. Operating temperature -430 C Operating pressure." Less than 14-00 D.S.i.

Gas evolut1on b ack reaction. a

Density (25 C.) 1.8a g./cc. Reactor vessel 1 Over-all volume 104.7 liters. VapQ fregion volume 7.3 liters. Critical region. volume filtiliters;

r I .r

Height of critical region; 2-l V Diameter of critical region. 14%". Vessel pressure limit 1400 psi.

91 0;D. with .006". gold. Water.

Coolant 4.36 gal, per minute.

: Coolant flow rate Coolant temperature 128 F. inlet. 600 F. outlet.

Coolant pressure 600 p.s.i. outlet, "Fuel solution circulation i velocity 1 ft. per sec.

Fuel burn-up -;compensation Vi around reactor vessel, or

burnabl poison. Excess pressure returns fuel Safety tonon-critical reservoir.

,Fastneutrons; Thermal neutronsn; 048x10 n/crnfi/see. aver- APPARATUS q The =pref erred embodiment' of the present": invention shown in Figure l comprisesa test tube shape'dreactor vessel 15, preferably. fabricated from stainless steel, clad with 0.0 15" gold," 'and having a' threaded top', flange Sealed to the topsurfaceof'theflan'ge I6,by* means of na ed Mar. 22, 19 0 Equal to r'ecombinatiorrby V 44 sniral coils. 21 ft. long. x 4;"? I.D.; clad l M own b l e graphite sleeve i 2.5 X 10 n/cm. /sec., average.

. merit sleeve 21.

' which is attached to a base 51.

3 an O ring or similar. device, is a steam outlet manifold plate 17. The plate 17 has a portion 18 which extends into the reactor vessel so as to provide a channel 19 through which extend steam outlet pipes 20. Extending upwardly from the lower portion 18 is a header attach- The header attachment sleeve 21 has sealed to its top a coolant inlet manifold assembly 22. The inlet manifold assembly 22 includes an inlet pipe suspending block 23, a manifold top plate 24 having a. chamber 25, and an inlet channel 26. A cover plate 27 is provided which engages threads on the periphery of the top of the header attachment sleeve 21 and which, through bolts and gaskets or similar means, seals the top plate 24 to the upper surface of header attachment sleeve 21. In this manner inlet pipes 28,.which extend from the heat exchanging apparatus 35, and which are sealed in the block 23, are connected to chamber and inlet channel 26. The inlet channel .26 is connected by conventional means to the coolant supply system, not shown.

Sealed to the upper surface of the outlet manifold plate 17 is an outlet manifold channel member 29 having a plurality of outlet connections 30 and forming a circular channel 31,. adjacentterminal point 32 of pipes 20. The terminalpoints 32 are welded or otherwise sealed to the outlet manifold plate 17.

A top plate 33, with a threaded portion which engages the threaded portion of the flange 16, has a cover 34 extending over the channel member 29. Bolts in cover 34 function to seal'the channel member 29, manifold plate 17 and the upper surface of flange 16 together .by means of 0 rings or similar devices.-

The outlet pipes 20' and inlet pipes 28 support heat exchanger 35. The heat exchanger 35 consists of 44 spiral coils, vertically stacked, each ,coil consisting of 21 feet of 7 OD. by Vs" I.D. stainless steel precious metal clad tubing. The heat exchanger is located in spaced relation to the bottom portion 18 of plate 17. Attached to and supported by the heat exchanger35 is a flow directing ba'ffle 'of platinum indicatedgenerally as 36 with a narrow neck portion 37 and a larger diameter bottom portion 38 connected by a sloping portion 39. The bottom of the baflie 36 is located about 6 inches from the bottom of the vessel for a vessel diameter of about 15 inches. The spacing, however, will depend upon the size of the reactor, the desired flow rate and the diameter of the bottom portion 38 of baffle 36.

At the bottom of the vessel 15 an opening is provided. Sealed to the walls of opening 40 is a liquid fuel transfer line 41.

flector 46 may be provided for'fuel burn-up compensation.

Cylindrical reflector 46 is vertically movable by hand or automatic means, and provides additional reflective material whichcan be moved to a position surrounding .the critical region after the reactor has been in operationfor some time to compensate for burn-up. How- .'ever, such a movable reflector would not be required if,

for example, burnable poison was used to compensate for reactivity changes over a period of time. Additional neutron reflecting material 47 is located immediately below the reactor vessel 15 and surrounds the liquid fuel transfer line 41. Located within the reflecting material 47 is a polonium-beryllium neutron source 48 which is used during initial start-up operations. A beryllium oxide block 49 is also located in the reflecting material 47. The block 49 becomes the primary background neutron source during subsequent start-ups.

The reactor vessel'15 is supported by a support 50 The base 51 also supports the reflector 45. The shielding construction and design are not described herein, since such construction and design are well known in the art.

LIQUID FUEL SYSTEMS Any liquid fissionable fuel having the following required characteristics is suitable for use with the reactor of the present invention:

1) The fuel vapor pressure increases substantially with increasing temperature in the operating temperature range;

(2) The fuel solution is chemically and radiolytically stable at operating temperatures;

(3) The fuel viscosity is sufliciently low to permit convection circulation at operating temperatures; and,

(4) The fuel density substantially decreases as the fuel is heated.

The liquid fuel utilized in the preferred embodiment of the reactor of the present invention is a solution of enriched uranium phosphate, phosphoric acid and water, such as the 0.3 M U0 in 17.5 M (95%) H PO solution illustrated in the above Summary of Reactor Specifications. This form requires the use of corrosion resistant cladding such as platinum, gold, or silver on all parts exposed to the solution at operating temperatures. The uranium is preferably enriched in the isotope U to a value of about 90 percent. This and other suitable fuel systems are described in more detail, and the parameter limits specified in co-pending application Ser. No. 589,835, filed June 6, 1956, entitled Nuclear Reactor Fuel Systems, now Patent No. 2.904,488, issued September 15, 19,59, the disclosure of which is incorporated herein by reference.

CRITICAL REGION The critical region of the reactor of the present invention is defined as that region within the lower portion of vessel 15 which extends downwardly from the bottom of the heat exchanger 35 to the bottom of the vessel 15, and is that region of the reactor vessel in which occurs the maximum concentration of neutron flux. The critical region, to a close approximation, is a right circular cylinder having a 14%" diameter and a 24 height. In the region located immediately above the critical region is the heat exchanger, the critical region and the heat exchanger region when filled with suitable nuclear fuel forming a critical assembly under normal operating conditions. Thus, under normal reactor operation, the liquid fuel level is near the top of heat exchanger 35. The-region between the top of heat exchanger 35 and manifold plate 17 and cxtending up into header attachment sleeve 21 is defined as the vapor region and is filled with vapor and a cover gas to be used as an overpressure to prevent boiling of the fuel and to assure valence stability.

The necessary conditions for criticality may be calculated by methods well known in the art with consideration being given; to the particular factors described above in the section, Liquid Fuel Systems. In any case, the term Critital Cegion" necessarily implies a uranium-moderator concentration in a critical geometry sufiicient to sustain a fission chain reaction.

LIQUID FUEL HANDLING SYSTEM shut-down operations. A vent 113 and coolant supply 114- are also provided for the coil 111.

The end of the reservoir 11% opposite to the liquid fuel transfer line 41 is connected to two branch systems at juncture 115. The first branch 116 extends ,througha pressure gauge 117, a flow limiting orifice 118, a shut-off valve 119, a reducing valve 129, and terminates at a gas anew-er r v 1.3. I V v supply 12!, hydrogen being used in thepreferre'd embodiment. t l V t The second branch .122 extends through relief valves 5123, which is by-passed by amanual valve 124, through a'charcoal trap 125, and is then vented tothe atmosphere.

A samplingtube 126 is connected to the reservoir 110 afthe end adjacent'liquid fuel transfer line 41, and extends through a valve 127 to conventional sampling apparatus 128. 7 i,

The operationof the above-described components will "become apparent from the hereinafter described operation "of the reactor.

LIQUID FUELCIRCULATTON l The liquid fuels utilized in the reactor of the present invention are circulated through'the heat exchanger :by convection current. .Figure 2 shows the general convection cycle. The liquid fuelwithin the critical-region, i.e.,

Q i I ,the region below -'the heat-exchanger 35, is heated ,by

nuclear fissions. The hot liquid 'rises.-up-channel 129- 'areacter "prpmpt criticalJ When s ufficient solution has been introduced into 'thereactor to reach the cold critical 7 volume, i. e.,"th at volumefof liquid fuel required for. the

solution to become critical and start to heat, the solution begins to heat up at such a rate that its negative temperature coeflicient (A -5.7x C.) uses up the excess reactivity produced by the further addition of solution.

The solution in the'core will continue to heat and expand' formed by the bathe bottom38 and i-passesqup' int o that.

portion of channel Informed by the-bafiieneck 37. The hotliquid fuel passes'bver the top of"bafiieineck 37 and into the heat exchanger 35. When the liquid fuel has reached a level approximatelyequal to the upper heat exchanger coil, operating temperature will then be reached, i.e., 430 C. At this condition, the vapor pressure of the fuel and the pressure due to compression'of the cover gas produces a total pressure which is the predetermined normal; operat ng pressure of the reactor. The pressure in line .130 and reservoir 110 is equal to the total reactor pressure since the hydrostatic head and the vapor pres I sure of the cold fuel in the reservoir arenegligible. When the predetermined operating pressure is indicated by gauge 117, valve 119 is' closedl" The convection cir'clilationisstarted by extracting heat A from the liquid fuel, This extraction is accomplished by into the spaces between the coil's offheat exchanger 35.

v ,The fuel then'passes down between the coils of heat exchanger into passage 130 which extends between the r sides of baffie bottom 38 and the wallsof reactor vessel 15.

' r The passage 130 has a total cross-sectional area approximately equal to 'the'cross-scction' area of the passagede fined by bafi1e-neck'37. As the liquid fuel passes into pas sage 130, it is within'the critical regionand is subiect'ed to a high neutron flux which causes fission; in the U thereby starting the process 'offheating the fuel. as itpasses down passage 130. The liquid fuel then passes around the bottom edge o f-lbaflle bottom 38 into the channel 129 where the fission and heating process is continued.

his obvious'that'the column of liquid, fuel in channel 129 is at ahigher temperature, and therefore ata lower density,tha'n the column of liquid fuel between the coils of heat exchanger 35 and passage 130. The difference in the density of the fuel in these two 'columnswprovides the convection flow. Theliquid fuel in the preferred embodimentcirculat'es at a velocity of about 1 ftt/sec. at full power. a

- OPERATION The initial startrupis carried out with movable reflector .46 raised to a position where it surrounds about twothirds of the critical region. The reactor vessel .15 and fuel reservoir 110 are evacuated by any conventional means; Valves 124 and 127 are closed (seeFig. 3). The

gas supply'12l is turned on by meansof valve 119 and the gas pressure from supply 121 passes through limiting 'orifice 118 and linelSfl into the reservoir 110, and. through line 41 intofreactor vcsse l 15'. Va1ve1'19 is closed when v the initial-' 'pressure of gas in 'thereservoir-re'actor system reachesthat pressure calculatedto give'thecorrectover-l pressurewhen compressed by the fuel under operating Ifconditions. lskilledtin the. art, is based upon the fraction of'the total volume'of the ;reactor vessel whichfth'e fuel isto occupy (The calculation, readily performed by one under operating conditions, the operating temperature,

2 Qpand the solubility of the' overpressure gas in the fuel.) f- Fuel .is then injected under pressure into the system through valvei127 and line 126. The volupie of fuel added'isjnotcritical, but must be of at leasta sufficient tion of thc volume of the reactor vessel under operating conditions; Any excess fuel will remainin the reservoir during operation of the reactor. Valve 127 is then closed and additional gas is admitted from hydrogen supply 121, thereby increasing the pressure and forcingfuel into the reactor. solution into the reactor to a saferate to prevent exceed- The limiting orifice 1 18 limitsjintroduction'of I rate of water flow'which maybe varied; The water in the {heat exchanger is-preferably highly purifiedby an ion- "flowing coolant water through the heat exchanger 35 thereby creating a temperature gradient in the liquid fuel.

The amount of heat extracted,'i.e., the rate of water flow through the heat exchanger, will determine the rate of convection circulation. Specifically for a water flow rate of 4.36 gals/min, the liquid fuel will circulate at a velocity;

of approximately'l ft./sec. y a

The polonium-beryllium source 48 is utilized merely to supply neutrons initially. The beryllium oxide block when irradiated with amma rays will supply additional neutrons for the reaction However, it should be noted that such devices are used to'facilitate control of the reactor during start-up operation, but are not required.

The power level of thereactor is controlled by the amount of heat removed from theheat exchanger, i.e. .'the

exchange bed. 'The'water is converted to steam within the heat exchang r." The steam output may be utilized in quantityto fill the aforementioned predetermined fracing a reactivity change of 10 cents/sec. (One cent is onehundredth of the dollar unit of reactivity'which, will make any conventional manner, i.e., heating, power production,

etc.

No control rods are required for the reactor of the present invention. Changes in reactivity resulting from fuel burn-up may be compensated'for by any conventional method, such as, (1) Adjustment in the position of a neutron reflector; (2.) Addition of fissionable material to the liquid' fuel;

.(3) Removal of moderator from the liquid fuel; and

(4) Utilization of a 'burnable poison. Y

It is within thepurview of this invention to'utilize any oneor all of these" methods to compensate for the fuel burn-up.

It should be noted that the adiustable neutron reflector 46fr'nayEalso befiised'for changing the reactor operating 7 temperature as well"asjcompensatingffor fuel burn-up. Self-regulation of the reactorisachieved through utilization of the "novel resilient pressurizing mechanism controlledbyreducingvalve and-relief valves 123w. This mechanism provides two distinct functions: (1') automatic "regulation of the volume of fuel in the reactorto maintain criticality upon variations in temperature'and-operating pressure,'and (2) automatic shut-down of the; reactor if the reactor operating pressure nears the predetermined vessel pressurelimit.

As explained above, liquid fuel .,will flow-from the reservoir tank 1.10 into reactor vessel 15 as long as the gas sure equilibrium will prevent the fuel contained in the reactor from draining back into-the reservoir tank. The direct communication of the reservoir tank with thereactor vessel, there being no valve in the fueltransfer line 41, results in resilient pressurization of the reservoir tank, thereby providing automatic regulation of the volume of fuel in the reactor. This is apparent since an increase in reactor internal pressure over the normal operatpressure results in a pressure differential from the gas contained in the reservoir tank, thereby causing fuel to drain from the reactor vessel back into the reservoir tank until pressure equilibrium is again established. Similarly, a drop in the internal pressure of the reactor below normal operating pressure will result in a pressure differential with the reservoir tank, thereby causing more fuel to be transferred from the reservoir tank to the reactor vessel until pressure equilibrium is again re-established. Since changes in fuel temperature result in changes in fuel density, thereby changing the reactor criticality, this selfregulating feature is also responsive to temperature as well as pressure variations. Because of this automatic self-regulating feature, there will normally be no interruption in the withdrawal of power from the reactor upon moderate variations in reactor temperatures and pressures, since the condition of criticality will be automatically restored.

If the reactor internal pressure exceeds a predetermined value, the relief valves 123 will allow gas present in the reservoir tank 110 to escape through the charcoal trap 125, thereby allowing the liquid fuel to flow out of the reactor vessel. The relief valves 123 are preset to allow the pressure within reservoir 110 to be vented to the atmosphere only if the internal reactor vessel pressure reaches a value close to the vessel pressure limit. Thus, under moderate pressure variations, the firstnamed self-regulating feature of the reactor will continue tooperate and the reactor will not be shut down. However, upon a large pressure build-up approaching the, vessel pressure limit, the reactor will be automatically shutdown through the operation of relief valves 123. Furthermore, should such a high pressure build-up in the reactor continue after all of the fuel has been drained from the reactor vessel back into the reservoir tank, the fuel itself will be vented to the atmosphere, charcoal trap 125 functioning to prevent an undesirable increase in atmosphere radioactvity. Manual shut-down of the reactor is accomplished by opening valve 124 to relieve the pressure holding the liquid fuel in the reactor.

Samples of the liquid fuel may be obtained by opening valve 127 and collecting a portion of the liquid fuel in the conventional sampling apparatus 128.

Thus it is apparent that the preferred embodiment of the present invention provides a simple, compact nuclear reactor which doesnot require constant attendance, since there are no moving parts within the reactor vessel, no control rods are required, and the reactor is self-regulating. Further, the present invention provides a novel arrangement and association.- of. parts which results in nuclear reaction which can be used at remote locations. While the presently preferred embodiment of the present invention has been described, it is clear that many. modifications may be made without departing from the scope of the-invention. Therefore the present invention is not limited by the foregoing description, but solely by the appended claims.

What is claimed is: n v p n 1. A homogeneous nuclear reactor comprising a sealed I reactor vessel having an' upper portionya middle portion and a lower portion, the upper end of said upper portion terminating in a removable manifold plate, heat exchanger means supported in said middle portion, said vessel'contaming a quantity of liquid fuel which during normal said vessel and to substantially fill the middle portion of said vessel thereby substantially covering said heat ex changer means and providing a lower boundary surface to define a vapor region extending between the level of said liquid fuel and/said manifold plate in said upper portion of said vessel, said .vapor region containing a cover gas at a predetermined operating overpressure, said fuel comprising'an' aqueous solution containing a sufficient concentration of a fissionable isotope to constitute a critical assembly when substantially filling the lower and middle portions of said vessel at said operating temperature, said fuel having a density which decreases with increases in fuel temperature above said operating temperature, said fuel having a viscosity sufiiciently low to permit convection circulation at said operating temperature, said fuel being chemically and radiolytically stable at said operating temperature, said fuel having a vapor pressure which increases with increases in fuel temperature above said operating temperature, means supported insaid lower and middle portions of said vessel for directing convection circulation of said liquid fuel through the lower portion of said vessel and around said heat exchanger means in the middle portion of said vessel, a fuel reservoir tank located externally of said reactor vessel, a fuel transfer line connecting said reservoir tank with the bottom of said reactor vessel, means for pressurizing said reservoir tank at said predetermined reactor operating pressure whereby under operating conditions the volume of fuel in the reactor vessel will be varied in response to deviations in reactor pressure from said predeterminedopera'ting pressure, and means for relieving the pressure in said reservoir tank when the reactor pressure reaches a predetermined upper limiting value.

2. A homogeneous nuclear reactor comprising a sealed reactor vessel having an upper portion, a middle portion and a lower portion, the upper end of said upper portion terminating in a removable manifold plate, heat exchanger means supported in said middle portion, said vessel containing a quantityof liquid fuel which during normal reactor operation at a predetermined operating temperature and pressure is sufiicient to fill the lower portion of said vessel and to substantially fill the middle portion of said vessel thereby substantially covering said heat exchanger means and providing a lower boundary surface to define a vapor region extending between the level of said liquid fuel and said manifold plate in said upper portion of said vessel, said vapor region containing a cover gas at a predetermined operating overpressure, said fuel comprising an aqueous solution containing a sufficient concentration of a'fissionable isotope to constitute a critical assembly when substantially filling the lower and middle portions of said vessel at said operating temperature, said fuel having a density which dccreases with increases in fueltcmperature above said operating temperature, said fuel having a viscosity sufficiently low to permit convection circulation at said reactor operation at a predetermined operating tempera- I i tureand pressure is stlfi cient to fill the lower'portion of operating temperature, said fuel being chemically and radiolytically stable at saidoperating temperature, said fuel havinga vapor pressure which increases with increases in fuel temperature above said operating temperature, means supported in said lower and middle portions of said vessel for directing convection circulation of said liquid fuel through the lower portion of said vessel and'caround said heat exchanger means in the middle portion of said vessel, a fuel reservoir tank located externally-of said reactor vessel, a fuel transfer line connecting Said reservoir tank with the bottom of said reactor vessel, means for pressurizing said reservoir tank "at said predetermined reactor operating pressure whereby .nnder operating conditions the volume of fuel in the reactor vessel will be varied in response to deviations in reactor pressure from said predetermined operating pressure, and a relief valve connected to said reservoir .tank,, Said-relief valve being adjusted to externally vent 9 the pressure in said reservoir tank when the reactor pressure reaches a predetermined upper limiting valve.

References Cited in the file of this patent UNITED STATES PATENTS 2,820,753 Miller et al. "Jan. 21, 1953 2,837,476 Busey June 3, 1958 2,843,543 Christy -c July 15, 1958 2,874,106 Hammond et a1. Feb. 17, 1959 m OTHER REFERENCES CF-53-8225, US. Atomic EnergyCommission document dated August 1953. Available from Atomic Energy '10 Commission Technical Information Service, Oak Ridge, Tenn. Pages 3, 7-20.

Procedures ofthe International Conference on the Peaceful Uses of Atomic Energy. Held in Geneva August 8-20, 1955, vol. 3, United Nations, N.Y. (1955), pages 283-286. An article by Froman, Hammond and King.

US. Atomic Energy Commission LA-1942. By L. D. P. King. April 13, 1955. Los Alamos Scientific Lab. Obtainable from Technical Information Services, Oak Ridge, Tenn. 17, 1955.

Pages 2-17. Date declassified August H 

1. A HOMOGENEOUS NUCLEAR REACTOR COMPRISING A SEALED REACTOR VESSEL HAVING AN UPPER PORTION, A MIDDLE PORTION AND A LOWER PROTION, THE UPPER END OF SAID UPPER PORTION TERMINATING IN A REMOVABLE MANIFOLD PLATE, HEAT EXCHANGER MEANS SUPPORTED IN SAID MIDDLE PORTION, SAID VESSEL CONTAINING A QUANTITY OF LIQUID FUEL WHICH DURING NORMAL REACTOR OPERATION AT A PREDETERMINED OPERATING TEMPERATURE AND PRESSURE IS SUFFICIENT TO FILL THE LOWER PORTION OF SAID VESSEL AND TO SUBSTANTIALLY FILL THE MIDDLE PORTION OF SAID VESSEL THEREBY SUBSTANTIALLY COVERING SAID HEAT EXCHANGER MEANS AND PROVIDING A LOWER BOUNDARY SURFACE TO DEFINE A VAPOR REGION EXTENDING BETWEEN THE LEVEL OF SAID LIQUID FUEL AND SAID MANIFOLD PLATE IN SAID UPPER PORTION OF SAID VESSEL, SAID VAPOR REGION CONTAINING A COVER GAS AT A PREDETERMINED OPERATING OVERPRESSURE, SAID FUEL COMPRISING AN AQUEOUS SOLUTION CONTAINING A SUFFICIENT CONCENTRATION OF A FISSIONABLE ISOTOPE TO CONSTITUTE A CRITICAL ASSEMBLY WHEN SUBSTANTIALLY FILLING THE LOWER AND MIDDLE PORTIONS OF SAID VESSEL AT SAID OPERATING TEMPERATURE, SAID FUEL HAVING A DENSITY WHICH DECREASES WITH INCREASES IN FUEL TEMPERATURE ABOVE SAID OPERATING TEMPERATURE, SAID FUEL HAVING A VISCOSITY SUFFICIENTLY LOW TO PERMIT CONVECTION CIRCULATION AT SAID OPERATING TEMPERATURE, SAID FUEL BEING CHEMICALLY AND RADIOLYTICALLY STABLE AT SAID OPERATING TEMPERATURE, SAID FUEL HAVING A VAPOR PRESSURE WHICH INCREASES WITH INCREASES IN FUEL TEMPERATURE ABOVE SAID OPERATING TEMPERATURE, MEANS SUPPORTED IN SAID LOWER AND MIDDLE PORTIONS, OF SAID VESSEL FOR DIRECTING CONVECTION CIRCULATION OF SAID LIQUID FUEL THROUGH THE LOWER PORTION OF SAID VESSEL AND AROUND SAID HEAT EXCHANGER MEANS IN THE MIDDLE PORTION OF SAID VESSEL, A FUEL RESERVIOR TANK LOCATED EXTERNALLY OF SAID REACTOR VESSEL, A FUEL TRANSFER LINE CONNECTING SAID RESERVIOR TANK WITH THE BOTTOM OF SAID REACTOR VESSEL, MEANS FOR PRESSURIZING SAID RESERVOIR TANK AT SAID PREDETERMINED REACTOR OPERATING PRESSURE WHEREBY UNDER OPERATING CONDITIONS THE VOLUME OF FUEL IN THE REACTOR VESSEL WILL BE VARIED IN RESPONSE TO DEVIATIONS IN REACTOR PRESSUURE FROM SAID PREDETERMINED OPERATING PRESSURE, AND MEANS FOR RELIEVING THE PRESSURE IN SAID RESERVOIR TANK WHEN THE REACTOR PRESSURE REACHES A PREDETERMINED UPPER LIMITING VALUE. 